Electron discharge device



1mg. 39, 1949. 5, FRANKEL ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 1 Filed Dec. 14, 1945 ATYD/P/VEY S. FRANKEL ELECTRON DIS CHARGE DEVICE Aug 3@, 1949.

Filed Dec. 14, 1945 2 Sheets-Sheet" 2 atentecl Aug. 30, 1949 UNITED STATES PATENT *OFFFIC-E 11 :Claims. 1 l invention relates to electron discharge devices, particularly to devices of the magnetron type.

Magnetrons have been proposed comprising -a "cathode, and an anode with a plurality of resonant cavities arranged around the cathode. Magnetic lines of force lengthwise of the cathode deflect the electrons into spiral paths around the cathode and successively past the cavity open- "'ings, which excite high frequency oscillations in the cavities. The preferred and most eiiici-ent operating mode, called the pi ('vr) modeycon'sists "of "excitation of alternate cavities in phase, this phase being opposite to that of the remaining cavities. When the cavities are not coupled to each other electrically, or are loosely coupled, several modes of operation in "addition to the desired 1r mode are possible. Unfortunately, the operating conditions, such as anode-cathode voltage and magnetic field strength, of the 'desired and undesired modes are not widely separated. That is,*'slight variations in operating condition can easily cause a change in themode of operation with "consequent changes "in efficiency, output and frequency. 'This'property of the magnetron is known asmode jumping? If "the modes can be widely separated as ire- 'gards operating conditions, then the performance of themagnetron tube becomes much less critical, and'in particular, if the 1r mode can'be separated from the others, stable operation in the most eihcient mode is insured. This separation of modes hasin the past been attempted invar'ious ways, including straps between alternate cavitities to'el'ectrically tie the cavities in parallel and insure the alternate phasing. At the higher Trequenc'ies straps are mechanically impractical and furthermore they introduce heavy capacitance loading between cavity walls.

In addition to proper electrical coupling between cavities, the magnetron Should have good electrical insulation between the parts carrying high frequency energy. When generating centi- "meter waves, for example, supports and electrode spacers of solid insulating material invariably introducehigh frequency losses, shunting capacitances and the like.

An object of my invention is .an improved electron discharge device of the magnetron type.

A further obiectof my invention is a magnetron that will operatein the most efficient mode, and yet will-be stable in that mode.

More specifically, an object of my inventionis .a magnetron that will operate in one modeand will not easily change to a different mode.

A still further object of my vinvent-i011 is amagnetron with electrodes that are rigidly supported and spaced without the usual high frequency losses of :solidinsulation.

, Embodiments tfor best illustrating the principles of my znovel magnetron are "described in the EfOHGV/itlg lspecificationgand shown in the iaccom- -panying'dr-awings in which Fig. 1 is :a-verticalsection, taken on line l- 'l oi Ei'gpz of one magnetron tuloe embodying my invention,

=Eig. .2 is .a asectionalview:on;line.2-2 ofFig. 1, Fig. 3 is a vertical section, taken on line -3-'-&3

of Big. 4. of another embodiment of my novel magnetron,

Fig. :4.is a sectional view on line 4--4 ofFig. 3,

and

Fig. '5 is a vertical half section *of still another embodiment 50f 'my novel magnetron.

My .n'ovel :ma'gnetron comprises a tubular cathode sleeve 1 aexteriorly .coated with an electron emissive layer :such as barium-strontium oxides "and internally heated with coil 2. "The ;:slee've-is coaxialwithamanode comprising a circle of vanes 'or :nns :3, extending radially outward router ends of the vanes terminate z'short .of the envelope wall, and the inner -5ends are evenly spaced :-a;round the circle called the :anode circle, with narrow slits or openings it :between each pair of vanes. Through these openings, the electron stream induces oscillating voltage in the cavities 5 bounded :round iron plugs'll-and it are set intcand sealed centrally in the envelope end plates. The-lower iron plug is tubular and internally accomodates a glass -button-'type header ll through which are sealed the cathode and cathode heater leads 12. The ends "of the yoke 13 of a permanent or electro magnet fit snugly against the iron plugs and establish a strong "magnetic held in the anpillar anode-cathode space with the magnetic lines of *force sllbstantially parallel to the cathode axis.

The va'nes are each individually supported, in the embodiment oiFig. lxon a metal stupor post -14 extending downward 'to the lower envelope and plate. Each vane 3 "andits stub support l t may conveniently, be stamped as a unit from relatively heavy gauge sheet metal, and the lower end of the support shaped into a right-angle foot I5 and brazed to the end plate. For electrical reasons, to be more fully described, the length of the stubs I4 is one quarter wave length at the operating frequency. Two cylinders l6 and I! are coaxial with the circle of supports, are placed respectively inside and outside the circle and are attached to the lower end plate. Cylinder I! is shorter in length than supports l4 so as to clear the lower edges of the vanes.

To operate, the necessary voltage is applied to the heating coil 2 to raise the sleeve to emitting temperature, and a high voltage, positive with respect to the cathode, is applied to the anode vanes. Preferably, the cathode is maintained at a high negative potential with respect to the anode so that the anode, and the connected envelope parts, may be grounded. Electrons which leave the face of the cathode are deflected by the axial magnetic field from the normal radial anode-cathode paths and. are caused to spiral about the cathode. By judicious adjustment of the field strength and anode voltage, the average electron may be made to encircle the cathode several times before falling into the cathode or anode. As the electrons traverse the cavity openings 4, the electrons bunch and exite oscillations in the cavities, and in the preferred mode, the electron transit time past the openings is so regulated with respect to the resonance property of the cavities, that the high frequency voltage across each opening is in phase opposition to the voltage across the next adjacent opening. Oppo- 1 site sides of each cavity may be considered as a transmission line, each line being coupled at the cathode end to an electromotive force with the electromotive forces of alternate lines in phase.

The end of each cavity remote from the voltage source is open physically and electrically, so that each cavity communicates with adjacent cavities around the ends of the vanes. Herein lies one of the important features of my invention. The open ended vanes insure close coupling, or heavy coupling, between adjacent cavities. The high frequency current flowing radially outward along one side of a vane must be equal to current flowing radially inward along the other side of the same vane. These two currents are actually and solidily connected in series around the outer end of the vane and must oscillate in exact phase opposition, independently of any interaction with the electron stream. Considerable variation may thus be tolerated in operating conditions, such as anode voltage and magnetic field, without disturbing this mode of operation. My method of insuring proper phasing is, essentially, to couple the cavities in series at the high current points, rather than, as usual, to couple the cavities in parallel at the high voltage points.

To insure the proper phase and voltage at the anode circle, for 1|- mode of operation, alternate cavities contain impedance disturbing elementsl8. These elements are small metal bars attached transversely across the sides of the vanes and function as lumped capacities shunted across the transmission line. When each cavity is considered as a transmission line of length 0 (the length of the vane), with characteristic impedance Z0 and when the disturbing element l8 introduces a capacitive reactance X0 in shunt with the line at a distance 02 from the anode circle or distance 01 from the outer end of the 4 vane, so that 01:19-02, then proper phasing and magnitude of the voltages is obtained if cos 0+cos (0 6 2 sin 0 2X, z In a magnetron of known construction, the factors 6, and Z0 are given directly and the necessary shunt reactance Xe for a given phase shift is determined by the high frequency properties of the line. Hence, the distance 01 or 02 may be solved from the above relation. Alternatively, an arbitrary value may be assigned to 01, or 02, and Xc solved for.

No electrical insulating material, except the single glass button H is necessary in my novel magnetron, yet the anode vanes are effectively isolated as to high frequency energy from all metal parts of the tube. The support stub for each anode vane is in effect the inner conductor of a resonant transmission line, the outer concluctor of the line being the cylinders i6 and H. The length of each stub is approximately one quarter wave length, and since the lower or envelope ends of the stubs and cylinders are short circuited, the opposite ends of the stubs present high impedance to the vanes. No interelectrode spacers, nor envelope spacers are necessary, and since all insulating material has been removed from the high frequency fields of the tube, heating losses and undesirable reactances inside the tube are eliminated.

An alternative anode support arrangement is shown in Figs. 3 and 4. The quarter-wave stub supports it for the vanes, here, extend radially outward from the vanes and are attached to the outer extremity of a flattened radial extension E9 of the envelope. The sides of the envelope extension are offset toward the stubs to provide the necessary spacing for transmission-line resonance and a standing voltage wave on the stubs. With the outer end of the transmission line short circuited, the impedance at the vaneend is a maximum Which, as before, permits operation of the vanes at high frequency without loss of energy to the supports.

The top and bottom end plates 1 and 8 of the envelope may, if desired, be moved into contact With the side edges of the vanes 3 as shown in Fig. 5. The outer ends of the vanes terminate short of the cylindrical envelope wall 8, and the inner ends lie in a circle close to and concentric with the cathode. The width of the openings between the inner ends of the vanes, and the distance from the cathode may be the same as in Fig. 1. The vanes and their cover plates can be enclosed in a separate envelope or may be hermetically sealed to and used as part of the envelope. The latter construction is shown. In operation, the spiraling electrons excite high frequency oscillation in the openings to the cavities, and the high frequency energy propagated lengthwise of one cavity is solidly coupled to the high frequency energy in the adjacent vanes through the openings at the outer ends of the vanes. The radial components of current in adjacent cavities are in exact phase opposition, as in Fig. 1, and the 'n' mode is insured even during considerable variation in operating conditions. While the enclosed passages or cavities of Fig. 5 may be theoretically treated as wave guides, and the open-sided passages or caviin that stable 1r mode of operation is insured with the close current coupling between cavities at their outer ends, and the 'voltage excitation of alternate cavities in phase opposition, attheir inner ends.

v My novel magnetron is stable in operation and efiicient. It will operate in the desired mode and will tolerate considerable variations in the parameters of the tube. It contains no powerabsorbing straps or insulators. My magnetron is simple and rugged in construction, and is easy to manufacture and operate.

I claim:

1. A magnetron comprising an elongated cathode, a plurality of evenly spaced metal vanes extending radially outward from said cathode, the inner ends of said vanes being spaced from each other and from said cathode, the space between each pair of vanes being in open communication around the outer ends of the vanes with the spaces of adjacent pairs of vanes, a metal envelope enclosing said cathode and vanes and everywhere spaced from said vanes, separate elements supporting each of said vanes from said envelope, and additional elements operatively associated with said separate elements forming infinite impedances therewith, and a magnet with poles at the ends of the cathode.

2. A magnetron comprising an envelope, a cathode mounted centrally in said envelope, a plurality of sheet metal vanes extending radially outward from said cathode, the inner ends of said vanes being evenly spaced from each other and from said cathode, a support stub for each vane attached at one end to one of said vanes and attached at its other end to said envelope, said stubs each being approximately one quarter wave in length at the operating frequency.

3. A magnetron comprising an anode structure having a plurality of elongated circularly arranged walls forming cavities, said Walls extending generally radially and each being open at its inner end and at its outer end, electronic means at the inner ends of said cavities for exciting oscillations in said cavities, a metal envelope enclosing said anode structure and said electronic means and everywhere spaced from said anode structure, separate elements supporting each of said anode walls from said envelope, and additional elements operatively associated with said separate elements forming infinite impedances therewith.

4. A magnetron oscillator comprising a tubular cathode, a plurality of sheet-metal vanes, one edge of each vane being parallel to and disposed in close spaced relation with the cathode, said vanes being uniformly spaced and extending radially outward from said cathode, an envelope enclosing said vanes and cathode, and everywhere spaced from said vanes, and separate elements supporting each of said vanes from said envelope and additional elements forming infinite impedances with said separate elements.

5. An electron discharge device comprising a cylindrical metal envelope, aligned iron plugs hermetically sealed centrally in the ends of said envelope, a tubular cathode between and coaXial with said plugs, a plurality of sheet-metal vanes in said envelope and circularly arranged in planes through the axis of said cathode, said vanes terminating at their outer ends short of the envelope wall, and separate elements supporting each of said vanes from said envelopes and additional elements forming infinite impedances with said separate elements.

6. An electron discharge device comprising a cylindrical envelope, round magnetic metal plugs hermetically sealed'centrally in the ends of said envelope, a cathode between and coaxial with said plugs, a plurality of evenly spaced sheet metal vanes in said envelope, said vanes extending radially outward from said cathode, said envelope having a flattened radial extension circumferential about the cylindrical side wall of the envelope, a support member attached to one of said vanes and tothe bottom of said extension, the length of said support member within said envelope extension being about an odd number of quarter wave lengths at the operating frequency.

7. An electron discharge device comprising an anode having a plurality of circularly arranged resonators having bounding walls and cavities therebetween, each cavity being radially elongated and in open communication at both ends with the adjacent cavities, electronic means at the inner ends of said cavities for inducing oscillations in said resonators through the openings at one end of the cavities, impedance disturbing elements for interrupting the continuity, to traveling electric waves, arranged on the walls of alternate cavities to shift the phase of said waves at said one end with respect to the phase of the waves at said one end of the remaining cavities, a metal envelope enclosing said device and everywhere spaced from said bounding walls, separate elements supporting each of said bounding walls, and additional elements forming infinite impedances with said separate elements.

8. An electron discharge device comprising a metal structure containing a plurality of walls defining elongated cavities, each cavity having an opening adapted for the induction of exciting voltages into said cavities, metal members mounted transversely across the walls of alternate cavities for changing the electrical impedance of said alternate cavities with respect to the electrical impedance of the remaining cavities, a metal envelope enclosing said device and everywhere spaced from said defining walls, separate elements supporting each of said defining walls from said envelope, and additional elements forming infinite impedances with said separate elements.

9. An electron discharge device comprising a structure having a plurality of resonators having walls defining cavities, the cavities having openings successively arranged and adapted to receive exciting voltages, impedance disturbing elements on the walls of alternate cavities to adjust the phase and magnitude of voltage at the openings of said alternate cavities, said elements comprising metal protuberances on and transversely across the side walls of the cavities, a metal envelope enclosing said device and everywhere spaced from said defining walls, separate elements supporting each of said defining walls from said envelope, and additional elements forming infinite impedances with said separate elements.

10. A magnetron according to claim 1 in which each of said elements of infinite impedance comprises a quarter wave length stub attached between the one of said vanes and said envelope and a conductor attached adjacent said stub to said envelope and forming with said stub a quarter wave length transmission line short circuited by said envelope.

11. A magnetron according to claim 1 in which said elements of infinite impedance comprise a quarter wave length stub attached between each of said vanes and said envelope, said stubs being 8 arranged in a circle about said cathode, and two UNITED STATES PATENTS cylinders coaxial with said circularly arranged stubs and attached inside and outside said circle 2 32 5 ggz z a1 g on said envelope, thus forming with said stubs 2404212 Bondley July 1946 quarter wave length transmission lines short clr- 5 Brown Dec. 1946 muted by Sam envehpe- 2,419,172 Smith Apr. 15, 1947 SIDNEY FRANKEL.

REFERENCES CITED The following references are of record in the 10 file of this patent: 

